Spot welded sheet material



Dm 1s, 1942.

M. WATTEFZ SPOT WELDED SHEET MATERIAL Filed Sept. 72,1%@

a Z m n A TTORNE Y fec. 15, 1942; M. lWAT-nena SPOT wELDED SHEETMATERIAL2 Sheets-Sheeai,

Filed Sept. '7, 1959 ATTORNEY Patented Dec. 15, 1942 SPOT WEIDED SHEETMATERIAL Michael Watter, Philadelphia, Pa., signor to Edward G. BuddManufacturing Co., Philadelphia, Pa., a corporation of PennsylvaniaApplication September 7, 1,39, Serial No. 293,751

2 Claims. (Cl. 148-12) The present invention relates to relievingelectrical resistance spot welded sheet material from temperature orWelding stresses resulting from such welding and to spot welded sheetmaterial having the weld stresses removed therefrom.

An object of the invention is to relieve spot welded sheet material ofweld stresses by subsequent cold working and the invention is applicableto both spaced spot welds, cr overlapping spot welds, as in a seam weld,whereby unsightly waves or bulges in the sheet metal parts between andadjacent the welds are substantially eliminated and the strength of theportion oi the metal softened by the welding is restored, thecold-working being effected at the welds to relieve temperature stressescaused by shrinkage oi' material at the welds.

Another object oi the invention is to accomplish the cold-working bypeening the metal at the welds in order to upset and spread the weldedportions oi' the metal an amount substantially equal to the shrinkagecaused by the welds.

A further object is to extend the peening perating in a continuous line,each peen overlapping another along the rows of welds for assuring inpractice the peening of every weld in a row and for applying the samedensity of peening on each weld for relieving the temperature stressesand for strengthening the metal equally at each weld throughcold-working throughout an entire IOW. v

A further object of the invention is to peenA along a row of slightlyspaced welds in hardened metal, said peening being performed at andbetween said welds in said row for causing a general elongation of themetal along and throughout the entire row of welds, the elongation beinggreatest at the welds and the total elongation being such as to restorethe original length of the material along the row existing pn'or towelding. l

A still further object is the provision of an extra layer of thinmaterial in the iormvof a backing strip extending along the lineoifff'welds and positioned to the side of either or both thin sheetmetal parts attached together by said welds, the welds extending throughsaid sheet metal parts and said backing strip or strips after which saidweldsare peened for restoring material strength and relieving stressestending to produce ripples or buckles in said thin sheet metal rts. pItis also an object of the invention to include a peening operation with awelding operation of simple nature, the apparatus for accomplishing thepeening being of a structure which may be manufactured economically, andwhich will eiliciently remove waves and buckles caused by the stresses`set up by welding.

With the foregoing and other objects in view which will be apparent asthe description proceeds, the invention resides in the method as well asthe construction and arrangement of parts, as hereinafter described andclaimed, it being understood that changes can be made within the scopeof what is claimed without departing from the spirit of the invention.

The invention is illustrated in the accompany@ ing drawings wherein:

Figure l is a perspective view showing the peening operation on sheetmetal parts spot welded together,

Figure 2 is a diagrammatic fragmentary plan of sheet metal partsindicating stresses caused by spot welding,

Figure 3 is also a diagrammatic view showiti the same, being a verticalsection on line 3-4 ci Figure 2,

Figure 4 is s view similar to Figure 3 showing the peening operationprogressed to the next row of welds,

Figure 5 is a perspective view showing peeping operation on thin sheetmetal parts, welded together,

Figure 8 is a fragmentary vertical section takenV on line i-I oi' Figure5,

Figure '1 is a perspective view showing the peening operation on sheetmetal parts, seam welded together with backing strips on opposite sidesof said thin sheet metal parts, and

Figure 8 is a sectional view of the same type of weld as shown in Figure'I being peened, with the shape of thethin metal parts being somewhatdiierent.

Referring to the drawings and more particu lai-1y to the form shown inFigures 1 to 4 inclusive, the numeral Il designates a unit of manu@facture consisting of a iiat extremely thin sheet H of stainless steelsuch as used for aircraft skin surface attached by means oi electricresist1 ance spot welding, as at I2, to a corrugated mem ber I3 alsomade of sheet stainless steel and slightly greater thickness. The spacedraised loops of the corrugated strip il adjacent the flat thin sheet ildetermine the space between the rows Il of welds, while the weide i2 ineach row M are spaced considerably closer together as clearly shown inFigure 1.

the character indicated which is oi exceptionally The shrinkage stressesresulting from weide it sheets H and i! together cause the thin sheet 5ito buckle between the rows of yields the saine being manifested by aconsideruble number of bulges and ripples, such as illustrated et il. Asthe sheet Il is of stainless steel with a highly polished reflectingsurface, unevenness in surface is greatly amplified in appearance and isexceptionally noticeable, thus presenting a surface very unpleasing tothe eye.

Such waves or ripples are produced by shrinkage each weld, which set upstresses pulling in all directions toward each. weld, the shrinkagetaking effect during the cooling after welding and being caused by theweld nugget being raised to a high temperature and being upset duringwelding, While bound in by relatively unheated metal, so that uponcooling, the nugget contracts, pulling the immediately surroundingmetal. Due to the extreme thinness and consequent lack of rigidity ofthe sheet H and the temperature stresses applied thereto, said sheet ilbulges at places slightly spaced from the welds and not subjected to thecontracting stresses, the spacing and association of the welds to oneanother deining the forms and characteristics of the .es produced.

previously stated, a purpose of the invention to relieve the stresses ateach weld in the thin sheet il to restore said sheet to its originalstate free from ripples or waves. In order to accomphsh the above bycold-working, one form peering apparatus is employed and as shown isconstituted by a pedestal Il having extending r" one side thereof a pairof arms II and il, carrying thereon a removable raised forming an anvilIl on which the i "este, while the other arm I1 supports an hommer il ofthe usual rapid reciprocating variety. Fitted to the hammer Il is apeening tool positioned directly above the anvil Il Vceiving between thesame and the anvil,

"erial il? to be worked.

sup-ply hose or tube It' leads to the air and has arranged thereon anair "im il gauge 28 for controlling etermining respectively the amountof air to the hammer, thus permitting s to assure peening strokes of thedesired amount of energy and rapidity for relieving the temperaturestresses of any particular metal or thickness thereof.

loco; ng the raised head forming the anvil l .a loop of the corrugatedsheet i3 nie will he properly positioned for backe peeping operation andthe loop of tion will act as a centering guide for l -ening tool 2i andthe anvil throughe entire roisr of welds in said loop for aanecold-worms of every weld through- -ot necessary to feed the unit ii inan itrent manner necessitating dwelling at but instead the unit il maybe grad n timing arranged wth respect .l oi the air hammer i! so thateach overlap the preceding blow. The peeping blows can be varied by ad.-regulating valve i9 so that pracno eect is had on the hardened coldstainless steel between the welds and only e welds where annealing andsoftening dus ding has occurred does the major portion sp "ng orupsetting of metal take place. re softer sheet metal is employed ig.action may elongate the nioby tween the welds as well as at the welds.In such a case, the total elongation along a line of welds should bringthe metal back in a substantially unstressed state to its originalunstressed length along that line prior to welding.

In Figures 2, 3 and 4 I have shown diagrammatically the problem aspresented and the manner in which the same is rendered. The bulges orwaves are exaggerated in size merely for the purpose of presenting aclear illustration. Figures 2 and 3 show the first two rows of weldsaandb as having been peened, said peening being indicated by theoverlapped circles p in Figure 2, while Figure 3 shows in addition tothese two rows, row c as peened. At the welds c and d in Figure 2 areshown arrows e indicating the temperature stresses and the directions ofpull of material in the thin sheet il towards the welds, thus producingbulges f (shown by dotted lines in Figure 2) formed by slack materialfree from temperature stresses caused by the welding. It will be notedthat the bulges appear greater at unattached places located betweendifferent welds. This is due to the fact that the stresses are short inlength and do not extend out a sufficient distance from the welds toexert pulls throughout the entire mass between welds. The lack ofstiffness due to the thin gauge of the sheet material Il causes saidsheet H to flex freeh, which is a prime factor in producing theundesirable bulges.

Spot welds, as well as seam welds, are usually arranged in rows with thewelds spaced a slight distance apart compared with the space betweendifferent rows of welds. This produces a general shrinkage along therows of welds leaving slack metal between the rows, which flexing causesthe waves or bulges as diagrammatically indicated in Figure 2.

As temperature stresses are responsible for the bulges, and annealing ofthe material at the Welds takes place at the time of welding, theannealed portions, including the weld nuggets, are advantageouslycold-worked by the peening to spread the anntelerA portions to relievethe temperature stresses for upon spreading the welds with the peeningprocess the annealed weld portions are cold-worked, resulting inrestoring the strength at such places.

Referring now to Figures 5 and 6 there is shown the peening processapplied to two pieces of thin sheet material 2| and 22 lapped over oneanother and seam welded along theline 1l. In this type of Weld thetemperature stresses also appear due to shrinkage along the line of thewelds which cause the thin sheets 2i and 22 to buckle forming waves orripples extending away from the welds, which gradually merge into oneanother and ilnally blend into the mass of material but not withoutleaving an unsightly appearance.

A peening apparatus of the same type as shown in Figure i having ananvil It and a peening tool 2! may also be used to spread the annealedwelded portions to relieve the temperature stresses. Remarkable resultshave been produced by peeriing on this type of weld.

Figure 't shows the peening apparatus used in connection with the sametype of weld shown in Figures 5 and 6 with the exception that backingstrips 24 and 2l are attached at the overlapped portions of the thinsheet metal parts 26 and 21 and the welds 28 extend also through saidbacking strips. This type of joint has been found very successful inconstructing fuel tanks of stainless steel sheet material for aircraftuse. The peening operation is applied in the same manner as described inthe previous forms with the same favorable results. It is to be notedthat while the sheet metal parts 26 and 21 are referred to asseparate'members, they may be the same piece oi sheet steel with itsopposite ends attached together to provide the cylindrical side wall ofthe fuel tank.

In Figure 8 the same type of weld Joint is illustrated as shown inFigure 7. However, in this figure I have shown the Joint as applied tothe flange 29 of a thin sheet metal wall and to a thin sheet member 3l.This type of construction may well be used in securing the end member tothe cylindrical wall member of a stainless steel tank. In this form theunsightly waves or ripples would not appear to an appreciable degree inthe member I0, but peening application has been found very desirable insuch form for the benefit of cold-working the welded portions andrestoring strength thereto to provide a sheet metal structure of uniformstrength.

It will appear that where the cold-working is applied to a seam weldsuch as in Figs. 5-8, inclusive, the continuous cold-working along thelength can be so adjusted as to substantially wipe out all trace ofstresses introduced by the welding and consequently the welded joint isstrengthened by the summation oi' internal stresses as well as by thecold-working. In the forms of Figs. 1-4. the continuous cold-workingalong a line of welds gives an overall increase in length to compensatefor such contraction as resulted from welding, but, since for practicalreasons each weld is not individually cold-worked, and the intermediatemetal is to some extent worked although so slight as to be hardlynoticeable in some instances, an approximation results which for allpractical purposes lends great improvement in the reduction of internalstress and to the appearance.

While several applications of the invention have been illustrated anddescribed and these y chieiiy in conjunction with stainless steel, it isto be understood that the invention is not to be limited thereto, butmay be applied in other forms as well and with other materials. As manychanges may be made in the construction and arrangement of parts as willbe apparent to those skilled in the art, reference will be had to theappended claims for a definition of the limits of the invention.

Having thus described my invention, what I claim as new is:

1. The method ottreating a thin gauge sheet o! metal having a row ofresistance welds therein which as a result of the stresses createdincident to the heating and cooling of the metal oi the welded regionsproduced distortions in the unwelded metal of the sheet normal to theplane thereof and beyond said regions, which consists in peening themetal of the sheet along the row of welds with the successive peeningsin substantially overlapping relation to permanently expand the same inthe plane of the sheet to remove the distortion producing stresses andthereby substantiallyrestore the distorted unwelded metal to its initialundistorted condition.

2. The method of treating a thin gauge sheet of metal having spaced rowsof resistance welds extending in the same general direction which as aresult oi! the stresses created incident to the heating and cooling ofthe welded regions in each row oi welds produced distortions in theunwelded metal of the sheet between said rows o! welds and normal to theplane of the sheet, which consists in peening the metal alone.r each ofsaid rows with the successive peeninss substantialb overlapping eachother to permanently expand the same in the plane of the sheetmnd indirections sumcient to remove the distortion Droducing stresses andthereby substantially restore the unwelded metal between said rows toits initial undistorted condition.

. MICHAEL WATTER.

